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diy solar

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Just my 2 cents, I made my own switch, is basic off/on with a resistor in between and is permanently mounted. I turn the switch on leave it on for a maybe 30 seconds then power up the Growatt then turn the pre-charge switch off and keep on trucking. You can add indicators if you prefer that but IMHO is not needed.
 
I'm curious, Do you plan the have the inverter disconnected from the battery often?
Is it 12V battery? if it is then you can use 470 Ohms resistor in series with a Red LED then put this assembly in parallel with your pre-charge resistor, this will be polarity sensitive for the LED to light up and it will light up very briefly depend on the capacitance of the capacitor bank inside the inverter..
 
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That will be fine, really no need to be precision 1% resistor since it is not critical circuit.
 
The one in Will's video looks to be 25W resistor, but 100% sure.
for 48V (it is actually around 55V), if you use 25 Ohms resistor, the max current will be 48V/25 Ohms = 1.9A so power dissipation on the resistor will be about 48V x 1.9A = 92W but it will be really really short duration so really no need to use 100W resistor, 50W will be fine, it takes 5 Tc (Time constant, you can look up RC time constant to learn about it) to charge the capacitor to the applied Voltage.
You can use 47 Ohms resistor in 12V/24V/48V with no issue, the resistor is used to limit the in-rush current, the time it takes to full charge the capacitor banks depend on the value of the resistor and the capacitance of the capacitor bank.
BTW, when perform pre-charge, the inverter power switch should in the OFF position.
 
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I made a setup similar to the first pic, used a small 12v rocker switch and alligator clips, throw the switch and wait a few seconds, done. Worked great.
 
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He also has a video showing how to use pencil to do pre-charge. Start @8:30 time stamp.
 
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